[PATCH bpf-next v4 3/3] selftests/bpf: xdp: test dev_xdp_install() rejects device-bound program

[Jiayuan Chen <jiayuan.chen@linux.dev>]

bpf_xdp_link_update() used to skip the checks in dev_xdp_attach(). Add a
test that makes a generic XDP link with a normal program and then tries
to swap in a device-bound program, which must fail.

Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
 .../bpf/prog_tests/xdp_dev_bound_only.c       | 49 +++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_dev_bound_only.c b/tools/testing/selftests/bpf/prog_tests/xdp_dev_bound_only.c
index 7dd18c6d06c6..4a13f8ec4300 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_dev_bound_only.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_dev_bound_only.c
@@ -1,9 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <net/if.h>
+#include <linux/if_link.h>
 #include <test_progs.h>
 #include <network_helpers.h>
 
 #define LOCAL_NETNS "xdp_dev_bound_only_netns"
+#define LINK_UPDATE_NETNS "xdp_dev_bound_only_lu_netns"
 
 static int load_dummy_prog(char *name, __u32 ifindex, __u32 flags)
 {
@@ -59,3 +61,50 @@ void test_xdp_dev_bound_only_offdev(void)
 	 */
 	SYS_NOFAIL("ip netns del " LOCAL_NETNS);
 }
+
+/* A device-bound program must not run on the XDP software path.
+ * dev_xdp_attach() rejected such programs, but bpf_xdp_link_update() reaches
+ * dev_xdp_install() directly and bypasses it, so the check has to live in
+ * dev_xdp_install(). Create a generic (SKB) XDP link with a normal program,
+ * then try to swap in a device-bound program via BPF_LINK_UPDATE.
+ */
+void test_xdp_dev_bound_only_link_update(void)
+{
+	LIBBPF_OPTS(bpf_link_create_opts, lopts, .flags = XDP_FLAGS_SKB_MODE);
+	int base_fd = -1, devbound_fd = -1, link_fd = -1;
+	struct nstoken *tok = NULL;
+	__u32 ifindex;
+	int err;
+
+	SYS(out, "ip netns add " LINK_UPDATE_NETNS);
+	tok = open_netns(LINK_UPDATE_NETNS);
+	if (!ASSERT_OK_PTR(tok, "open_netns"))
+		goto out;
+
+	SYS(out, "ip link add eth42 type veth");
+	ifindex = if_nametoindex("eth42");
+	if (!ASSERT_NEQ(ifindex, 0, "if_nametoindex"))
+		goto out;
+
+	devbound_fd = load_dummy_prog("devbound", ifindex, BPF_F_XDP_DEV_BOUND_ONLY);
+	if (!ASSERT_GE(devbound_fd, 0, "load_dummy_prog devbound"))
+		goto out;
+
+	base_fd = load_dummy_prog("base", 0, 0);
+	if (!ASSERT_GE(base_fd, 0, "load_dummy_prog base"))
+		goto out;
+
+	link_fd = bpf_link_create(base_fd, ifindex, BPF_XDP, &lopts);
+	if (!ASSERT_GE(link_fd, 0, "bpf_link_create"))
+		goto out;
+
+	err = bpf_link_update(link_fd, devbound_fd, NULL);
+	ASSERT_EQ(err, -EINVAL, "link_update device-bound rejected");
+
+out:
+	close(link_fd);
+	close(base_fd);
+	close(devbound_fd);
+	close_netns(tok);
+	SYS_NOFAIL("ip netns del " LINK_UPDATE_NETNS);
+}
-- 
2.43.0